1. Field of the Invention
The present invention relates to an image taking device and a method of controlling exposure, and in particular, to a technique for controlling exposure at the time of picking up an image.
2. Description of the Related Art
Hitherto, there has been made a proposal that exposure is controlled with reference to the distribution of brightness in a screen (refer to Japanese Patent Application Laid-Open No. 2003-295251). In addition, Japanese Patent Application Laid-Open Nos. 2004-235956 and 2004-341901 disclose a technique in which picked up image is subjected to backlight correction processing.
The technique disclosed in Japanese Patent Application Laid-Open No. 2003-295251 is such that exposure is adjusted to one of a bright and a dark part in the screen. The technique, however, has a problem in that overexposure or underexposure is caused in the entire screen when the area of the bright or the dark part in the screen to which exposure is adjusted is smaller than that of the entire screen.
The technique disclosed in Japanese Patent Application Laid-Open Nos. 2004-235956 and 2004-34190 has such a problem that it lacks in scene toughness because, when a backlight state (a state where a background is brighter than a main object or a difference between contrasts in an image is large) is determined, and unless patterns do not match with each other, it is not determined that it is in a backlight state. Japanese Patent Application Laid-Open No. 2004-235956 describes that a luminance distribution histogram is formed. The process of the histogram is so complicated that it is caused a problem in that it is difficult to process the histogram in real time (for example, through image display).
The technique disclosed in Japanese Patent Application Laid-Open No. 2004-341901 is such that a determination is made based on a percentage of dark picture elements to bright picture elements whether or not a picked up image is a backlit figure image. The technique consumes much time in process for determining lightness on a picture element basis, which causes a problem in that it is difficult to process in real time. Japanese Patent Application Laid-Open No. 2004-341901 has also such a problem that it does not specifically describe an image process suited for a backlit figure image.